Hello, my name is Bill Marston. I am a vascular surgeon at the University of North Carolina. Also the director of the Chronic Wound Healing Limb Preservation Center here. It's a real pleasure to be involved in the American Academy of Dermatology's wound care course. And my task is to teach you about the rational use of vascular studies for patients with wound and wound healing issues. So we'll be talking about the use of vascular studies such as duplex ultrasound, CT, MRI, and physiologic testing to look at the arterial and venous systems. We'll mainly focus on the lower extremities because that's where the large majority of chronic wound healing issues occur. So when thinking about vascular tests, in general we're trying to determine whether symptoms in the leg, whether it's pain, claudication, swelling, poor wound healing, are related to dysfunction within the vascular system. And we want to sometimes determine if we're going to perform procedure like a MOS or some other procedure in the limb, whether there's enough blood supply to heal the wound. And if a patient presents with a chronic wound, do they have blood supply and good enough venous function to heal the wound. In general, we're going to separate this into the arterial system, the venous system, and the lymphatics. And testing may be preferred to give us anatomic information about where there are areas of dysfunction in these systems or hemodynamic information concerning how bad the dysfunction is. And these are two distinct questions that require different types of testing. So first, let's focus on evaluation of the arterial system. And again, key questions are where is the disease and how severe is it? Will this wound heal after surgery or with medical management? There are a variety of methods to evaluate the arterial circulation in the lower extremity. But a question many ask is, what about palpation of the blood vessels in the foot? Is this adequate? So really, the question depends on how good the evaluator is and how experienced they are. So if you can feel easily palpable blood vessels in the foot in the dorsalis pedis artery or the posterior tibial at the ankle, and you feel that you know what a normal blood vessel palpation should feel like, then that is likely adequate. But for many who don't have a lot of experience in palpation of blood vessels, it's smart to go ahead and get another method to determine the adequacy of circulation. And this could include ankle brachial index, Doppler waveform analysis, toe pressures, transcutaneous PO2, and or laser Doppler. Now, a general recommendation would be, if you're going to get any studies in a vascular lab with any frequency, would be to develop a relationship with that laboratory. Different vascular labs report information in different ways. And often, interpretation is required of the studies, and it may not be obvious to you as a non-vascular specialist. So my advice is to seek out the medical director of a lab that you will be using so that they can serve as a resource to you when you're attempting to interpret the studies that you are provided. An ankle brachial index is a useful non-invasive method that can be performed in many outpatient settings, as long as you have a blood pressure cuff and a handheld Doppler device. This is performed by inflating the blood pressure cuff in the ankle while obtaining a signal from either the posterior tibial or dorsalis pedis artery at the ankle. As the pressure cuff is inflated, the pressure at which the signal is obliterated indicates the ankle pressure. This is compared to the brachial artery pressure, and a ratio is obtained. Normally, the pressure should be the same, or the ankle pressure may be slightly higher. As long as the ratio is greater than 0.7, there is likely adequate blood supply to that lower extremity to be sufficient for healing. And patients generally would have relatively mild symptoms of claudication, if any, in the limb. A ratio of 0.5 to 0.7 is considered questionable for adequacy of healing. Patients may have more severe claudication or rest pain at that level. And an ankle brachial index of less than 0.5 typically indicates severe peripheral arterial disease, and wounds would have trouble healing at that level. The problem with ankle brachial indexes is that if the arteries in the lower extremity are significantly calcified, they are not easily compressed with the blood pressure cuff, thus leading to false elevation of the pressure in the lower extremity blood vessels. So if the ankle brachial index is greater than 1.2, you should disregard the ratio and obtain another method of non-invasive evaluation. This typically requires referral of the patient to a peripheral vascular lab. And a general and very important consideration is that if you are going to refer patients for vascular testing, it will be very important to develop a relationship with the laboratory so you can understand the results that they are forwarding to you, and to be sure that you get the correct studies performed to treat your patient appropriately. I would recommend finding the medical director of any lab you will be working with and developing a relationship with them as there often are questions concerning the studies performed. Arterial segmental studies are a method to use duplex ultrasound imaging and B-mode ultrasound to image vessels at different stations down the leg. Typically, the blood vessels are evaluated in the common femoral, the superficial femoral, the popliteal, and the tibial arteries. And waveforms are obtained as noted in the slide. This then requires the physician interpreting the study to examine the waveforms to determine if these are normal or not. This slide indicates normal waveform in the top left, which is identified as a triphasic signal with a brisk upstroke. The signal returns below the baseline, and then a third component with arterial rebound. This indicates normal blood flow in vessels that have this type of signal. A biphasic signal on the top right is also considered to be indicative of good flow, although maybe not completely normal. On the bottom left, when you see monophasic signals with delayed upstroke, this indicates evidence of a significant obstruction in the artery above the level of incination. And a non-pulsational signal indicates severely deficient blood flow. So by performing this type of waveform analysis, the interpreter can provide information on the location and severity of the arterial obstruction. In patients who have calcified vessels and an ankle brachial index is not able to be obtained, often toe pressures can be performed because the toe blood vessels are rarely severely calcified. This requires the use of a toe blood pressure cuff and a sensitive Doppler probe. A normal reading would be greater than 80 millimeters of mercury, and in a subsequent slide we'll discuss what lower readings indicate. Other options to obtain hemodynamic information on the lower extremity blood vessels include transcutaneous oximetry. This device is best performed with multiple leads in different locations of the lower extremity, and normal levels would be a transcutaneous PO2 of greater than 70 to 80 millimeters of mercury. It is useful to predict response to hyperbaric oxygen in which an oxygen challenge is administered. If the oxygen levels increase significantly, this often predicts a good beneficial response to treatment in a hyperbaric chamber. Laser Doppler to obtain a skin perfusion pressure can also be performed. This measures the local microcirculatory blood pressure using a toe cuff and laser sensor, and this determines the pressure required to obstruct microcirculatory flow, usually performed in a toe. In a meta-analysis of studies performed with laser Doppler devices, a cutoff of 30 millimeters of mercury provided an 80% chance of wound healing with levels above this cutoff. So, I would say that all of these methods can be useful, but none of them have a very high sensitivity and specificity to predict healing. So, we typically use this type of chart. This is really a key slide to focus on. It looks at all these modalities and their relationship to healing potential. So, if you have an ankle brachial index that is greater than 0.7, waveforms that are triphasic, toe pressure greater than 50, and either a TCPO2 or a laser Doppler, skin perfusion pressure greater than 30, these are related to high healing potential. Conversely, levels lower than this, and particularly very low levels, are related to low healing potential. We typically try to obtain multiple studies to maximize our predictive capability. Typically, we might combine waveform analysis with a toe pressure or a TCPO2 to give us the best indication. Obviously, there are limitations, as we said, calcified vessels in patients with diabetes and renal failure significantly limit analysis. Some patients have limitations with prior surgery in the foot, toe amputations and such, and patients with certain skin deficiencies, thickening, are difficult to obtain skin perfusion pressures. So, we advise using multiple modalities. Vascular labs have most, if not all, of these modalities to use in treatment decision making for you. Most of the time, sufficient information can be obtained from the methods previously described, but occasionally additional information is required due to contradictory studies or other considerations and actual imaging is requested. Most often, this is done when we are considering vascular reconstruction to provide additional anatomic information on the sites and severity of obstruction. In this situation, CT imaging and MRI imaging can be beneficial and often depends on the individual radiology department as to their level of expertise in these techniques. In general, actual imaging is better for proximal arteries because they are larger with less calcification and the more distal arteries below the knees. Limitations to CT tomography include contrast allergy or renal insufficiency and MRI also can have contrast issues, but most often is dependent on local expertise. It's important to note that hemodynamic information is generally not provided from axillary imaging, so determination of adequacy of blood flow is better performed on the physiologic tests that were described previously. In summary, I think it's critical to define the question that you are asking before obtaining arterial imaging. Are you interested in whether a patient's symptoms are due to arterial insufficiency? Are you wondering if a wound will heal or one of your surgical procedures will heal? If you wish to develop your own expertise, palpation or use of a handheld Doppler to do ankle brachial index can allow you to evaluate patients yourself in your clinic. However, in general, use of a peripheral vascular lab will be necessary and it's critical to communicate with that lab so they understand the question that you are asking. If you're interested in claudication, let them know that. They can specifically test the patient for that. If you're interested in whether a wound on the foot will heal, then information such as toe pressures or skin perfusion pressure in that area of the wound is very beneficial. Once you've worked with a lab for a while and they understand your needs and you understand how they're interpreting the information, it will significantly improve your results with these types of patients. Let's move over to the venous system. Evaluating the venous hemodynamics and function even more so requires communication with the vascular laboratory. The reason being that if you send a patient to the lab and you ask them to do a venous study on the leg, the likely response you will get is a study that is interpreted as there is no evidence of acute deep vein thrombosis. Understand that this is the question that the vascular lab is asked the vast majority of times that they are asked to do a venous study. You likely are not interested in that question. Your key question would be, is there obstruction? Is it acute or chronic? Is there reflux? And how severe is this disease? Again, your question may be, is venous disease causing the patient to have leg swelling? Is it inhibiting a wound like this shown on the slide from healing? And the lab needs to know what your specific questions are to give you the best information possible. This picture indicates really the critical person here, which is the vascular technologist. They have a range of tests that I'm going to describe with which to evaluate the venous system. And depending on your questions, they will use these tests to maximize the information they provide. The first phase of a complete duplex venous test is performed in the supine position. In this position, the technologist evaluates the patient for obstruction or thickening, which would be consistent with prior venous thrombosis in the deep and superficial system. They will look for incompetent perforator veins that communicate the deep and superficial system. This is typically done supine with some degree of reverse Trendelenburg position, and the knee is partially bent, as noted here. The scan looks at the deep veins, as noted. And you can see in the image of the iliac vein a small bit of what looks like thrombus layering in on the superior margin of the vein. Sometimes they will be able to identify anatomic variability in the venous system that is more common than the arterial system. They also evaluate the superficial system, again, for anatomic variability, such as duplicate great saphenous vein variability in the saphenopapoteal junction, presence of prior interventions, such as ablations or sclerotherapy. Perforators occur at numerous different levels in the leg. It's fairly time-consuming and exhaustive to look for all of these perforator veins, so understanding what you as the clinician are interested in allows them to tailor the exam for perforators in these areas. For instance, if a patient has a leg ulcer in the medial ankle area, we typically look for perforators in the medial calf and ankle, not in other locations. This image shows a large perforator vein communicating the deep and superficial system. These are tests for abnormal flow. Flow should all move from the superficial into the perforator vein. Reverse flow that moves out of the deep system into the superficial is abnormal. So by compressing and releasing, they look for outward flow. If this occurs for longer than 0.5 seconds after this compress and release, that would be pathologically abnormal. There are lots of perforators in the leg. In general, we would consider perforator veins smaller than 3 millimeters to be clinically insignificant at causing symptoms. Large perforators greater than 3 millimeters with outward flow are capable of causing poor wound healing, lipodematous sclerosis, and similar symptoms. This image shows on the left side image A at the time of release a large amount of reverse flow. On the right, image B is a smaller amount of reverse flow. Both would be identified as being abnormal because both are greater than 0.5 seconds of reverse flow. However, image A is going to be much worse in terms of hemodynamic impact because the velocity and length of reflux are longer. So it's important to look at the actual images to interpret how much hemodynamic deficiency is being caused by the finding in the perforator vein. The next area of examination in the supine position is to look for outflow obstruction in the iliac veins or inferior vena cava. These typically occur in patients after prior deep vein thrombosis in the proximal veins. An outflow obstruction, if it's severe, can cause marked limb edema and poor wound healing. The image on the left shows a static flow velocity through the common femoral vein. This would indicate a high likelihood of outflow obstruction. Normally, there should be respiratory variation, as noted in the image on the right, and changes in the velocity of flow with augmentation. Another method of looking for iliac vein obstruction is to directly examine the vein with B-mode ultrasound and color flow, as indicated in the slide here. The technologist can look for elevated velocities at a site of stenosis, and using the color flow and power doppler can look for direct stenosis on the scan. This technique can be somewhat limited in patients with obesity or bowel gas that obstructs the veins, but if the vessels can be visualized, it is a useful technique. Clearly, this requires a significant degree of experience and expertise in the hands of the technologist performing the study. The other component of a full venous evaluation is to perform a standing reflux scan. This is to assess for abnormal reflux in the veins due to poor valve function. The patient stands with the leg offloaded, and the technologist images the vessel evaluating flow while the leg is compressed and released below the site of incination. This can be done using a hand squeeze and release, or with an automatic rapid inflation deflation blood pressure cuff. The cuff is placed inferior to the vein segment being tested, and it is inflated to 100-150 millimeters of mercury, and then rapidly deflated, inducing reflux in the venous segment. In the presence of normal valve function, this reflux should cease within less than half a second. This slide shows normal and abnormal venous reflux tracings on the left. You can see with compression, there is forward flow, and then at release, it's just a very short blip of reverse flow, and then no additional flow within the vein. Compare this to the vessel on the right that shows forward flow with compression, and at the time of release, there is prolonged reverse flow that extends for more than several seconds without the valve eliminating this reverse flow. The reporting out of this information may be done in different ways by different labs, but this would be a report that shows normal valve function in the deep veins, the common femoral, the femoral, and the palpiteal vein, and abnormal function in the great saphenous both at the sapheno-femoral junction and at the knee. So this would indicate the patient has superficial venous insufficiency only in the greater saphenous vein, but throughout the great saphenous vein. This would be a report of a different patient that has deep and superficial venous insufficiency with abnormal valve closure times in all of the segments examined except for the small saphenous vein. So as you can see, this is an extensive evaluation of the entire venous system serving the lower extremity, and it provides both an assessment of obstruction as well as valvular function. It would be useful in determining whether a patient's symptoms are related to venous system dysfunction and what the capability of healing is from venous disease. Again, you would have to specifically request this study from the lab if you wish to get information other than the presence of acute deep vein thrombosis. The one thing this assessment does not provide is a global assessment of how severe the venous dysfunction is. Now if there's more sites of reflux, then generally the severity is going to be higher. But if you really want to know how severe the dysfunction is, this will require other methods of evaluation such as plethysmography. However, currently most venous centers don't perform plethysmography very often. They usually treat patients based on the findings on the venous duplex study alone. However, if you really want to get more human anatomy information, you could consider the use of photoplethysmography or aeroplethysmography. These are methods to measure volume changes in the limb. And they use a specific testing method to identify the severity of venous dysfunction. PPG is based on the determination of the optical properties of a single point skin area using non-visible infrared light that's emitted into the skin. Depending on the amount absorbed, it is able to measure the volume of the blood within the skin itself. Test is performed by elevating the leg, thereby unfilling the veins in the leg and the volume goes down. The patient then stands up and the speed of refilling of the veins is measured. Refilling should occur slowly if there is normal valve function. So on the top tracing, you see a relatively slow refilling phase that is normal. Patients who have valve dysfunction have a faster refilling phase since the valves do not close properly. The speed with which this occurs can be related to the severity of venous disease using a parameter called the venous filling index. In this study performed in 1988, the venous filling index was correlated to the incidence of leg swelling, skin changes, and ulceration. Other imaging modalities that can be considered would again be axial imaging with CT or MRI. Typically these are performed in cases where duplex is not able to be performed successfully such as morbid obesity and pelvic venous obstruction or if the duplex imaging and symptoms do not correlate. It's atypical anatomy in patients who have unusual perforator veins, Klippel-Trenonay syndrome, or other anatomic venous abnormalities can be studied with axial imaging to provide additional information. Also we often do this type of imaging if we are planning venous reconstructive procedures for patients with iliac or vena cava abnormalities. So in summary, duplex ultrasound is clearly the workhorse of venous evaluation. It allows us to evaluate for venous obstruction, poor valve function, and to determine options for procedural intervention. Astrophy is infrequently utilized but can provide information about hemodynamic severity of disease similar to an ankle brachial index for arterial disease. And axial imaging is used to supplement most often for patients with obesity or who are undergoing venous reconstructive procedures. Lymphatic disease is not often studied with imaging testing. Most often if we feel that a patient has lymphedema as a cause of poor wound healing, we study for venous disease. And if this is excluded, patients are generally considered to have some amount of lymphatic disease and treatment is initiated for this, typically with compression, elevation, manual lymphatic decongestive therapy, or intermittent pneumatic compression. If a patient might be considered a surgical candidate for lymphatic procedures, then we would consider obtaining a lymphocentogram. And this is a study where a radioactive tracer is injected into the limb, usually in the foot, and this tracer is concentrated in the lymphatic vessels. Over several hours, repeated imaging will study the elimination of the radioactive tracer through the lymphatic channels. We generally only would consider doing these for patients where we're considering a corrective procedure. My suggestion would be to identify a physician who does these procedures and usually obtain the studies to facilitate that physician's evaluation of the patients. In our practice, it's not common that we do these procedures. So I hope this information has been helpful to you in determining how vascular lab testing can help in your patients with wound care issues. I'd like to thank the American Academy of Dermatology for inviting me to participate in the course, and thank you for your attention.

vascular studies

wound care

lower extremities

duplex ultrasound

arterial evaluation

venous hemodynamics

lab collaboration